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571.
《中国航空学报》2023,36(3):80-95
A direct numerical simulation of hypersonic Shock wave and Turbulent Boundary Layer Interaction(STBLI) at Mach 6.0 on a sharp 7° half-angle circular cone/flare configuration at zero angle of attack is performed. The flare angle is 34° and the momentum thickness Reynolds number based on the incoming turbulent boundary layer on the sharp circular cone is Reθ = 2506. It is found that the mean flow is separated and the separation bubble occurring near the corner exhibits unsteadiness. The Reynolds analogy factor changes dramatically across the interaction, and varies between 1.06 and 1.27 in the downstream region, while the QP85 scaling factor has a nearly constant value of 0.5 across the interaction. The evolution of the reattached boundary layer is characterized in terms of the mean profiles, the Reynolds stress components, the anisotropy tensor and the turbulence kinetic energy. It is argued that the recovery is incomplete and the near-wall asymptotic behavior does not occur for the hypersonic interaction. In addition, mean skin friction decomposition in an axisymmetric turbulent boundary layer is carried out for the first time. Downstream of the interaction, the contributions of transverse curvature and body divergence are negligible, whereas the positive contribution associated with the turbulence kinetic energy production and the negative spatial-growth contribution are dominant. Based on scale decomposition, the positive contribution is further divided into terms with different spanwise length scales. The negative contribution is analyzed by comparing the convective term, the streamwise-heterogeneity term and the pressure gradient term. 相似文献
572.
《中国航空学报》2022,35(9):379-388
Material properties play an important role in the performance of electromagnetic mechanism. For an aeronautic Hermetically-Sealed Electromagnetic Relay (HSER), more than 50% parts are made of soft magnetic materials. Therefore, the performance of soft magnetic materials directly determines the static and dynamic characteristics of the HSER. Based on the theory of crystal recrystallization, this paper analyzes cold extrusion and heat treatment in the processing of soft magnetic materials, simulates the grain change process of an armature at different heat treatment temperatures, establishes a correlation model of temperature, grain size, and magnetic energy, and verifies results by scanning electron microscopy. Results of heat treatment temperatures from 800 °C to 920 °C are obtained and compared. A sample soft magnetic material after heat treatment at different temperatures has the largest difference in the initial magnetization range, up to 22%. In order to verify the fluctuation of the overall output characteristics of an HSER caused by the difference between soft magnetic materials, a static and dynamic analysis model of a typical HSER is established, and the accuracy of the model is verified by a set of actual test system. The difference of dynamic characteristics under different heat treatment temperatures is nearly 3%. 相似文献
573.
城市热岛效应是当前城市生态领域关注的焦点问题之一。本文以上海为例,基于FY-3C/VIRR LST数据,通过计算研究区的热岛强度指数与热岛比例指数,定量分析上海市2019年全年城市热岛效应的时空变化特性。结果表明:上海市2019年全年各月份的总热岛区域面积均在40%以上,城市热岛效应较为显著,其中7月份总热岛区域面积最大;上海市热岛效应的空间分布呈现出“北热南冷”的格局,热岛效应主要分布在中部和北部; 上海市5—7月热带比例指数较高,为较严重热岛,随着8月份平均地表温度的继续升高,热岛比例指数有所下降。 相似文献
574.
《中国航空学报》2022,35(12):102-116
Mechanically pumped two-phase loop (MPTL) which is a prominent two-phase heat transfer technology presents a promising prospect in thermal control for space payload. However, transient behavior of MPTL caused by phase-change and heat sources load-on/off in simulated space environment is rarely reported. In the present study, one MPTL setup was designed and constructed, and experimentally studied. Particularly, a novel two-phase thermally-controlled accumulator integrated with passive cooling measure and three capillary structures was designed as the temperature-control device. Dynamic behavior of the start-up, temperature control, and temperature adjustment were monitored; meanwhile, thermodynamic behavior within the proposed accumulator, the operating behavior as well as the heat and mass transfer behavior between the main loop and the accumulator were revealed. The results show that the fluid management function of the capillary structures for the novel accumulator is verified. The working point of the MPTL system can be adjusted by changing the temperature control point of the accumulator and it is little influenced by external heat flux and heat sources on/off. Pressure-drop oscillations which are manifested as fluctuations of temperature and pressure can be observed after phase changing due to the compressible volume within the accumulator and the negative-slope portion of the internal pressure. 相似文献
575.
为开发具有良好防隔热和力学性能的高性能石英纤维毡,基于传热数学方程,预测了石英纤维毡的厚度对其隔热性能的影响规律;为提高纤维毡的力学性能,探究了在纤维毡中添加不同层数的石英纤维布对其力学性能的影响规律;此外还探讨了针刺密度对石英纤维毡隔热性能和力学性能的影响。结果表明:石英纤维毡传热模型与实验吻合度可达94.8%;石英纤维毡厚度提升2 mm,其隔热性能提高20 ℃左右;添加石英纤维布可以显著提高纤维毡断裂强力和撕破强力;针刺密度可以提升纤维毡力学性能,但针刺密度过大会破坏纤维毡结构,使其力学性能下降。 相似文献
576.
577.
以热防护系统隔热组合结构中不同隔热材料厚度尺寸为计算变量,以飞行器主结构温度极值即最低背面温度为目标参数,以组合结构中第二层材料最高使用温度为约束条件建立隔热组合结构模型,并进行了石英灯考核验证。采用通用软件ANSYS 进行一维瞬态有限元热分析,将模型计算结果和试验结果进行了全面对比,各项数据吻合良好。 相似文献
578.
579.
《中国航空学报》2023,36(3):212-219
Infrared camouflage based on artificial thermal metasurfaces has recently attracted significant attention. By eliminating thermal radiation differences between the object and the background, it is possible to hide a given object from infrared detection. Infrared camouflage is an important element that increases the survivability of aircraft and missiles, by reducing target susceptibility to infrared guided threats. Herein, a simple and practicable design is theoretically presented based on a multilayer film for infrared stealth, with distinctive advantages of scalability, flexible fabrication, and structural simplicity. The multilayer medium consists of silicon substrate, carbon layer and zinc sulfide film, the optical properties of which are determined by transfer matrix method. By locally changing the thickness of the coating film, the spatial tunability and continuity in thermal emission are demonstrated. A continuous change of emissive power is further obtained and consequently implemented to achieve thermal camouflage functionality. In addition, other functionalities, like thermal illusion and thermal coding, are demonstrated by thickness-engineered multilayer films. 相似文献
580.
Flow control using surface Dielectric Barrier Discharge(DBD) plasma actuators driven by a sinusoidal alternating-current power supply has gained significant attention from the aeronautic industry. The induced flow field of the plasma actuator, with the starting vortex in the wall jet,plays an important role in flow control. However, the energy consumed for producing the induced flow field is only a small fraction of the total energy utilized by the plasma actuator, and most of the total energy i... 相似文献